Ceramic frame grid



Dec. 31, 1957 w. R. WHEELER 2,818,522

CERAMIC FRAME GRID Filed April 19, 1954 INVENTOR k 1 444 W/lL/AM 1?.Will-ELM ATTORNEY United States PatentO CERAMIC. FRAME GRID William R.Wheeler,wan'tagh, N..,assignor to Sylvania Electricllroducts Inc., acorporation .of--Massachusetts Application April 19, 1954, Serial No.424,225

4 Claims. (Cl. 313268) This invention relates to grid structures such asare employed in vacuum tubes.

The growth of the electron tube manufacture art has progressed to whereit is possible to utilize automatic machinery to assemble the componentparts of a tube. To lend itself toward such manufacture, tubes have beendesigned wherein the electrodes are stacked one above the other withinsulating spacers therebetween. To lend toward compactness of parts,reduction in number of parts and improvement in tube performance, it hasbeen found desirable to integrate electrodes with the spacers. It istoward these objectives that this invention is directed.

To make a tube with suitable characteristics it is necessary that thespacers shall be of high electrical resistance for preventing leakage,thin for compactness and strong for ruggedness. Ceramics have been foundto meet these specifications. One of the better ceramics for thispurpose is zircon, the silicate of zirconium, although alumina andsteatite have also been found to be useful. But in the past it has beenfound to be exceedingly difficult to effect a proper bond between theceramic material and a metal, such for example as the metal of gridlaterals of a grid structure. I have discovered that by suitably coatinga ceramic support or spacer with a molymanganese composition andsubsequently utilizing a proper brazing compound, I can effectivelysecure grid wires or other electrode structure to the ceramic materialand particularly where the ceramic material is zircon.

I have also discovered that in the past shorts have occurred between thegrid laterals and closely adjacent cathode because of the sagging of thegrid wires when the cathode was heated. This I found was due mainly tothe different coeflicients of expansion between the material of the gridsupport and the grid wire material. I have overcome this deficiency byassociating with my selected grid support structurea zircon frame-wiresmade of tungsten since tungsten has very nearly the coefiicient ofexpansion of Zircon.

My invention will be better understood after consideration of thefollowing specification and the exemplifications of my inventiondisclosed in the accompanying drawings in which Fig. 1 discloses a formof integrated insulating spacer and grid,

Fig. 2 discloses another form of integrated spacer and dual electrodestructure including an anode and a grid,

Fig. 3 is a perspective view showing the back of the structure of Fig.2, and

Fig. 4 is an enlarged view similar to Fig. 2 but with a portion brokenaway to better show end recesses.

Referring to the drawings in greater detail, at there is disclosed awafer-like rectangular hollow ceramic frame preferably of zircon havingon its face 12 a molymanganese coating 14. This coating may be formed byapplying a moly-manganese powder to a surface of the zircon and firingthe same at 1350 C. for ten minutes in a wet hydrogen atmosphere. Mosteffective results have been obtained if rather a dilute suspension ofthe powder 2,818,522 Patented Dec. 31, 195? consisting i of 'about 80%molybdenum and manganese be painted onto the surface of the zircon andthen surface,-nor be dark nor *have a-glazed appearance. If

such be thecase the suspension is too dense. Withsuffic'ien't-"dilution, it will be found 'that the fused surface adheres'stronglyenoug'h'to' tlre ceramic surface even during -theprocess-subsequently employed to'attach the tungsten grid nvires 16 tothe fused surface.

The suspension is painted only onto the surface of the ceramic to whichthe grid wires are to be attached, for example, the surface 12. In orderto secure the tungsten wires to the molymanganese coating on the zircon,a brazing compound including a wetting agent for both the metals of thecoating and the grid is necessary. Such a brazing compound is, forexample, one utilizing a nickel plated gold-silver alloy, the brazingbeing accomplished in a moist hydrogen atmosphere, and the nickel beingthe wetting agent. Also attached to the coating on the ceramic is themolybdenum tab 18 for connection with a suitable terminal in the tube,the molybdenum tab being attached to the ceramic in the same manner asthe tungsten Wires.

The tungsten wires may conveniently be formed on the ceramic by placingtwo ceramics back to back with the coated faces outermost, winding atungsten wire about both ceramics, brazing the wire in place and thenwith a stiff brush brushing off the wires where they do not adhere tothe ceramics. The wire in the manufacture of very small tubes is of veryfine diameter and may easily be picked off from the ceramics near theedges of the same Where not attached to the ceramic. Each of the twopieces of ceramic now forms a grid structure.

The form shown in Figs. 2, 3, and 4 differs from that in Fig. 1 in thatthe ceramic 20 not only serves to support the grid wires 22 on themetallized surface 24 but also serves to support an anode moly-manganesecoating 30 on the bottom of a recess in the face of the ceramic, thewalls of the recess serving as insulating media between the bottomcoating 30 and the grid structure. To further insure insulating theanode coating from the grid surface, the ceramic is slitted through asat 32, the slits in effect forming continuations of two of the walls ofthe recess. Also the lateral ends of the recess are deepened as at 33for the same purpose. Anode pins 34 passing through the ceramic andbrazed to the coating 30 are provided for connecting the bottom coatingwith tube terminals. The grid structure is provided with a molybdenumtab 28, as in the case of the structure of Fig. 1.

Having thus described my invention, what I claim as new is:

1. A combined grid, anode, and insulator comprising a rectangular waferof ceramic material with a recessed face, a metallic coating at thebottom of the recess forming an anode, and a terminal connected with theanode, the wafer at two opposite boundary edges of the anode havingslots through to the back of the wafer, a second metallic coating on theface of the wafer and a grid structure integrated with the secondmetallic coating and spanning the recess.

2. A combined grid, anode, and insulator comprising a rectangular waferof ceramic material with a recessed face, a metallic coating at thebottom of the recess forming an anode, and a terminal connected with theanode, the wafer at two opposite boundary edges of the anode havingslots through to the back of the wafer, the wafer at the other two edgeshaving further recesses a second metallic coating on the face of thewafer and a grid structure integrated with the second metallic coatingand spanning the recess.

3. A combined grid, anode, and insulator comprising a rectangular waferof ceramic material with a recessed face, a moly-manganese coating atthe bottom of the recess and a terminal connected therewith andextending beyond the wafer, a second moly-manganese coating on the faceof the wafer surrounding the recessed portion and a grid structureintegrated With the second coating and spanning the recess.

4. A combined grid, anode, and insulator comprising a rectangular waferof ceramic material with a recessed face, a moly-manganese coating atthe bottom of the recess and a terminal connected therewith andextending beyond the water, a second moly-manganese coating on the faceof the wafer surrounding the recessed portion, a grid structureintegrated with the second coating and spanning the recess, and tabstructure connected with said second coating.

References Cited in the file of this patent UNITED STATES PATENTSSchottky May 12, Le Van June 12, Gormley et a1. Oct. 24, Sorg July 28,Sorg July 20, Doolittle Nov. 1,

FOREIGN PATENTS.

Great Britain Apr. 5,

